For some types of cardiac pacing leads, it can be difficult to determine how well the fixation mechanism or pacing electrode is contacting tissue. For example, for a lead having a fixed or extendable helix, there may be no easy to interpret indicator visible in fluoroscopy that the helix has turned and penetrated the tissue. While the fact that the helix is fully extended may be determinable, the number of turns of the helix that have entered the heart's tissue may be unknown.
With new therapies such as LV endocardial pacing, lead revisions become more difficult and lead fixation becomes increasingly important. During implant of these types of leads, it would be especially desirable to precisely determine when the helix is fully fixed in the myocardium using available pacing-related parameters.
To address this issue, a number of systems have been proposed and/or developed. For example, monitoring of impedance levels associated with the helix and/or other electrodes as the helix is screwed into tissue is disclosed in, U.S. Pat. No. 6,714,086 issued to laizzo et al. and incorporated herein by reference in its entirety. An alternative approach is based upon measurement of current of injury (COI) as disclosed in U.S. Pat. No. 6,714,086 issued to Cholette, also incorporated herein by reference in its entirety.